It is now common for such winches, particularly those of the manually powered type, to be provided with a plurality of drive ratios between their drive input and the winch drum. Interchange between the various drive ratios is normally achieved by reversal of the direction of drive input causing an automatic interchange, without reversal of the direction of rotation of the drum.
One common type of winch has three drive ratios of increasing mechanical advantage the lowest being a 1:1 ratio, i.e. a direct drive and the other involving gear trains, with interchange being by reversal of the drive direction as discussed above. However, if the interchange from the ratio of the lowest mechanical advantage to the next ratio up is determined by the relative directions of rotation of drive and drum, there is a risk that the ratio of lowest mechanical efficiency would be disengaged if the drum overruns. Overrunning is a common event, so it is important that this should not change the drive ratio.
In our U.S. patent specification No. 3973755 we disclosed a winch having three drive ratios, the first being a 1:1 ratio, in which the position of a resiliently loaded actuator determined whether the drive shaft of the winch was engaged directly to the drum or was disengaged. The resilient loading normally forced the actuator to its engaged position, but the winch also had a catch on a stationary part of the winch which engaged the actuator only when the actuator moved with the drive shaft in one direction. When this catch engaged the actuator, the actuator was forced from its engaged position, against its resilient loading, to its disengaged position, at which position it was held by a detent. On reaching this position the actuator became disengaged from the catch. Since the catch was on a stationary part of the winch, disengagement occurred only when there was a reversal of rotation of the drive shaft in an absolute sense, not merely relative to the drum. In order to release the actuator from its detent, and so re-engage the 1:1 drive ratio, the disengagement means accessible to the operator was provided on the winch.
When the winch is used with the sheet of a sail of a sailing vessel, the first (1:1) drive ratio is very useful when tacking because it permits the sheet to be tensioned rapidly when the sail is "flogging". In this situation there is virtually no force applied by the sail to the sheet and so it can be pulled easily. Once the tension has been set up in the sheet, reversal of the drive engages the second ratio and the higher mechanical efficiency enables the tension in the sheet to be increased. Finally, a second reversal engages the third ratio and enables the sheet to be pulled to its final position, at which the tension is very high. When the vessel tacks again, the tension is again released and so operation of the disengagement means enables the winch to return to the first ratio.
Such a winch is of less use, however, with a spinnaker. The sheet of such a sail is never slack and so the 1:1 ratio is of little use. Medium and high tension can be handled by the second and third ratios, but for low tensions a ratio with a slightly greater mechanical advantage is needed. Therefore winches are designed to meet this purpose in which all ratios involve direct transmission through gear trains.
Clearly, the ratios of such a winch may be selected to be suitable for a spinnaker, but then the winch is of less use during tacking.